Provided are a pharmaceutical composition for treating an FLT3 mutation-positive cancer； a mutant FLT3 inhibitor； and uses thereof. Disclosed are a pharmaceutical composition for treating an FLT3 mutation-positive cancer, containing a compound represented by General Formula [1] or a salt thereof as an active ingredient； a mutant FLT3 inhibitor； an anticancer agent； a method for predicting a therapeutic effect by administration of a pharmaceutical composition containing a compound represented by General Formula [1] or a salt thereof in a subject, including a step of detecting the presence or absence of an FLT3 mutation； a method for selecting a subject to whom a pharmaceutical composition containing a compound represented by General Formula [1] or a salt thereof is applied, including a step of detecting the presence or absence of an FLT3 mutation； and a method for determining whether or not a pharmaceutical composition containing a compound represented by General Formula [1] or a salt thereof is administered to a subject, including a step of detecting the presence or absence of an FLT3 mutation.
